1. Field of the Invention
The invention relates to a gas turbine engine heat exchanger and a method of its assembly to the engine.
2. Prior Art
Gas turbine engines which utilize the Brayton Thermal Cycle for automotive and industrial applications have been the subject of intense engineering study for nearly 50 years. What has evolved is a simple cycle consisting of an air compressor, a combustion section in which an air-fuel mixture is burned to form hot gases that reach 1600 degrees Fahrenheit temperature or greater. These hot gases are directed to the turbine sections to produce rotary motion which drives the air compressor and an engine output shaft. After the hot gases have passed through the turbine sections and prior to their being exhausted from the engine, it is desirable to extract as much heat as possible from the exhaust so as to reduce the fuel consumption of the engine. This is accomplished by transferring the heat energy from the hot exhaust to the relatively cooler compressed intake air prior to its mixture with fuel and subsequent burning in the combustion chamber. The most popular type of heat exchanger used to accomplish this heat energy transfer is a regenerator which employs a rotating cylindrically shaped disk or drum.
Typically, a regenerator consists of a core which is either made from ceramic or metallic material. The core permits the flow of gases through a plurality of passages formed in the material. The hot gases exiting from the turbine section are passed through the passages of one sector in the regenerator core in one axial direction and the core material is heated. As the core is rotated, the absorbed heat is transferred to the incoming cooler compressed air which passes through the same sector of the regenerator in an opposite direction. As a result, less fuel is burned in the combustion chamber to heat the compressed air to the desired turbine inlet temperature.
This cyclic thermal loading on the regenerator matrix causes the core to distort and bow or dish slightly from the desired parallel plane condition to a concavo-convex condition, the cooler face being concave and the hotter face being convex. This warping condition causes a variable dimension relationship between various elements of the mechanism which is used to rotatably drive the regenerator core. This results in excessive wear and noise which is particularly objectionable in industrial and automotive engines. Thus, the choice and the design of the regenerator drive has been severely restricted and the economy of its structure has been sacrificed.
In a regenerator system, an annular metal drive member in the form of a ring gear surrounds the exterior periphery or cylindrical surface of the core. Because the annular metal drive member and the regenerator core may have substantially different thermal coefficients of expansion, they are normally designed not to be in contact with one another. For this reason, the annular ring is spaced from the regenerator core member, and a resilient member is provided for transmitting torque from the annular drive member to the regenerator core.
The resilient member for transmitting torque from the drive ring to the regenerator core has taken several forms in the prior art. In U.S. Pat. No. 3,363,478 to Lanning, U.S. Pat. No. 3,401,741 to Paluszny et al., U.S. Pat. No. 3,430,687 to Wardale, U.S. Pat. No. 3,534,807 to Bracken and U.S. Pat. No. 3,693,703 to Stockton, the resilient members comprise various forms of springs compressed between the ring gear and the regenerator core. Resilient members in the form of elastomeric materials compressed between the inner surface of the drive ring gear and the periphery of the regenerator core are described in U.S. Pat. No. 3,525,384 to Horton, U.S. Pat. No. 3,586,096 to McLean, U.S. Pat. No. 3,666,000 to Blech et al., U.S. Pat. No. 3,741,287 to Mittman and U.S. Pat. No. 4,151,873 to Lewakowski. None of the above approaches have been found to be satisfactory in retaining the ring gear onto the core and some have created other problems such as core cracking, elastomer bond failure, high torsional wind-up and seal failures.
In regenerative automotive and industrial gas turbine engines, there have been numerous attempt to solve the core failures experienced due to the uneven fluid and/or thermal forces on the rotating disk. For example, in U.S. Pat. Nos. 3,985,181 and 4,057,102, Guillot uses a tie rod to connect the outer regenerator cover and the frame of the main housing together to prevent cover blow-out. Guillot also reduces the effect of hydraulic forces by reducing the sector of the cooling air to be heated by the regenerator core to 120 degrees. None of the prior an designs have solved the problem of regenerator core distortion and pinching of the core between the engine housing and the exhaust covers due to the uneven thermal expansion of the mating components which results in excessive core drag, wear and noise as discussed in U.S. Pat. No. 3,177,735 to Chute. Because of these problems, the commercial success of regenerative gas turbine engines has been limited.
In practice, none of the prior art designs have been found to be satisfactory because the thermal expansion of the different components and the different fluid forces which act on the system have been difficult to analyze. None of the above cited prior art designs have recognized the need to isolate the regenerator core from the engine main housing so as to minimize the interaction of the thermal expansion of the housing with the heat exchanger system, the need to control both the fluid and thermal forces acting on the core and finally the need for a regenerator drive system that is independently controlled from the main engine drive system.